Method of writing servo signal on magnetic tape

ABSTRACT

A method of writing servo signals on a magnetic tape which comprises irradiating one end of an optical fiber bundle ( 12 ) comprising a plurality of optical fibers ( 11 ) arrayed in parallel with each other with laser light, transmitting the laser light ( 24 ) emitted from the other end as an output light source through a condensing lens ( 13 ), and irradiating a site of a magnetic tape running at a prescribed speed, the site being capable of forming servo tracks, with the laser light passed through the condensing lens ( 13 ) to form real images ( 25 ) equal to or smaller in size than the output light source to cause the site to change physically or chemically thereby forming a plurality of servo track patterns (S) in the longitudinal direction of the tape at a smaller pitch than the pitch of the optical fibers ( 11 ) arrayed in the optical fiber bundle ( 12 ).

TECHNICAL FIELD

The present invention relates to a method and an apparatus for writingservo signals on a magnetic tape, by which servo tracks can be formed ata small pitch.

BACKGROUND ART

One of means for increasing the recording capacity of magnetic tape isto increase the density of data tracks. However, as the track densityincreases, the distance between adjacent data tracks is shortened, andit becomes more likely that the magnetic head strays off the rightposition during data recording or reproduction, failing to keep accuracyof recording or reproduction. Various servo tracking systems have beenproposed to address this problem.

One of typical servo tracking systems for magnetic tape is formation ofservo tracks corresponding to servo signals on a magnetic tapemagnetically or by mechanical stamping. According to this system, thesmaller the distance between servo tracks formed, the more accurate theservo control. To achieve this, however, a complicated or large-sizedapparatus is required.

Accordingly, an object of the present invention is to provide a methodand an apparatus for writing servo signals on a magnetic tape which willmake it possible to easily form a large number of servo tracks at asmall pitch.

DISCLOSURE OF THE INVENTION

The present invention accomplishes the above object by providing amethod of writing servo signals on a magnetic tape which comprisesirradiating one end of an optical fiber bundle comprising a plurality ofoptical fibers arrayed in parallel with each other with laser light,transmitting the laser light emitted from the other end as an outputlight source through a condensing lens, and irradiating a site of amagnetic tape running at a prescribed speed, the site being capable offorming servo tracks, with the laser light passed through the condensinglens to form real images equal to or smaller in size than the outputlight source to cause the site to change physically or chemicallythereby forming a plurality of servo track patterns in the longitudinaldirection of the tape at a smaller pitch than the pitch of the opticalfibers arrayed in the optical fiber bundle.

The present invention also provides an apparatus for writing servosignals on a magnetic tape, which is preferably used to carry out theabove-mentioned method, which comprises a system for running magnetictape, a system for writing servo signals on the magnetic tape(hereinafter, servo signal writing system), and a light source systemproviding laser light incident upon the servo signal writing system,wherein:

the servo signal writing system has an optical fiber bundle where aplurality of optical fibers are arrayed in parallel to each other withthe center axes of the individual optical fibers being coplanar and acondensing lens which receives the laser light emitted from the end ofthe optical fiber bundle, the optical fiber bundle and the lens beingdisposed such that the direction in which real images of the outputlaser light source formed through the lens are aligned and the runningdirection of the magnetic tape may make an angle larger than 0° andsmaller than 90° when viewed from above.

The present invention also provides an apparatus for writing servosignals on a magnetic tape which comprises a system for running magnetictape, a system for writing servo signals on the magnetic tape(hereinafter, servo signal writing system), and a light source systemproviding laser light incident upon the servo signal writing system,wherein:

the servo signal writing system has a group of two or more optical fiberbundles each having a plurality of optical fibers arrayed in parallel toeach other with the center axes of the individual optical fibers beingcoplanar, the optical fiber bundles being superposed on each other insuch a manner that real images may be formed at a smaller pitch than thepitch of real images formed by the individual optical fiber bundles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a first embodiment of the servo signalwriting apparatus according to the present invention.

FIG. 2 is a schematic cross section showing the structure of an opticalfiber bundle.

FIG. 3 schematically shows the way of forming servo tracks on magnetictape, seen from above.

FIG. 4 is a schematic view of a servo signal writing system in a secondembodiment of the servo signal writing apparatus according to thepresent invention.

FIG. 5 schematically shows another mode of a servo signal writing systemin the first embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be hereunder described with reference to itspreferred embodiments by way of the accompanying drawings. FIGS. 1through 3 illustrate a first embodiment of the servo signal writingapparatus according to the present invention. As shown in FIG. 1, theapparatus has a magnetic tape running system (not shown), a servo signalwriting system 10 for writing servo signals on the magnetic tape 1, anda light source system 20 providing laser light incident on the servosignal writing system 10.

The magnetic tape running system comprises a feed reel having a magnetictape, on which servo tracks are to be formed, wound therearound, atake-up reel for taking up the fed magnetic tape, and a driving meansfor revolving these reels. These members are set to make magnetic tape 1run in direction A. Such a running system has the same mechanism as thatin a conventional magnetic tape recording and reproducing drive. Whilenot shown, the running system also has a means for regulating eitheredge of the running magnetic tape 1, by which fluctuation of the runningmagnetic tape 1 in the width direction may be prevented thereby to keepthe distance from that edge to each servo track pattern constant.

The light source system 20 for laser light comprises as many modules 21as optical fibers hereinafter described, each module having a laserdiode optically connected to each optical fiber, driving means 22 fordriving the individual laser diodes, and connectors 23 which opticallyconnect the individual modules 21 to an external fiber bundle. Thedriving means 22 is electrically connected to a controller therefore(not shown) composed of an oscillator, etc. and operates according tothe instructions given from the controller. The operation of the drivingmeans 22 makes the laser diode in each module 21 emit light at aprescribed time interval.

The servo signal writing system 10 comprises an optical fiber bundle 12where a plurality of optical fibers 11 are arrayed in parallel with eachother with their center axes being coplanar and a condensing lens 13having a large aperture which receives and converges output laser light24 emitted from the emission end of the optical fiber bundle 12. Theincidence side end of the optical fibers 11 are optically connected tothe respective connectors 23 of the light source system 20. Thecondensing lens 13 is capable of capturing 70% or more, preferably 95%or more, of the output laser light 24 emitted from the emission end ofthe optical fiber bundle 12. The condensing lens 13 is disposed at sucha position as to form real images 25 on the site of the running magnetictape 1 where servo tracks can be formed (on the backcoating layer 5 inthe present embodiment), the images 25 being equal to or smaller in sizethan the output light source, i.e., the line of spots of emitted laserlight 24 (aligned output laser light 24), preferably 0.8 or smallertimes as large as the output light source. In other words, thecondensing lens 13 constitutes a reduction projection optical system.

As shown in FIG. 2, the optical fiber bundle 12 comprises a lower flatplate 14 of prescribed thickness having on one side thereof many grooves17 (preferably V-shaped) which are straight and parallel to each other,optical fibers 11 put in the grooves 17 one by one, and an upper flatplate 15 covering the optical fibers 11. The groove 17 are such that thecenter axes of the individual optical fibers 11 may be coplanar. Thegrooves 17 are provided at such a regular interval that the distancebetween every adjacent optical fibers 11, i.e., the pitch P₀ of theoptical fibers 11 may be equal to the diameter of the optical fibers 11.

The optical fiber bundle 12 is disposed such that the direction in whichthe real images 25 of the output light source which are formed throughthe condensing lens 13 on the magnetic tape 1 are aligned (i.e., thedirection of the line of spots of the output laser light 24 emitted fromthe optical fiber bundle 12) and the running direction of the magnetictape 1 may make an angle θ (see FIG. 3, described later) larger than 0°and smaller than 90° in their plan view. In detail, the optical fiberbundle 12 is disposed in such a manner that the direction in which theoptical fibers 11 are arrayed to make up the optical fiber bundle 12 istilted at an angle larger than 0° and smaller than 90° with the magnetictape 1 running direction in their plan view.

The method for forming servo tracks on the magnetic tape 1 by the use ofthe above-described apparatus is hereinafter explained. The laser diodesof the modules 21 in the light source system 20 are made to emit lightat a prescribed time interval. The emitted laser light enters therespective optical fibers 11 and is emitted from the emission end of theoptical fiber bundle 12. The emitted laser light 24 passes through thecondensing lens 13 and irradiates the backcoating layer 5 of themagnetic tape 1 running at a prescribed speed. As a result, real images25 are formed on the backcoating layer 5, which images are equal to orsmaller than the line of spots of the output laser light 24 at theemission end of the optical fiber bundle 12. The irradiated part of thebackcoating layer 5 undergoes a physical or chemical change to form aservo track pattern along the longitudinal direction of the tape. FIG. 3shows formation of real images 25 on the backcoating layer 5 by whichservo track patterns are formed. In FIG. 3, arrow A is the magnetic taperunning direction, and line B is the direction of the aligned spots ofthe output laser light as real images 25. Symbols L's each indicate theirradiation position of the output laser light in the image 25 formed onthe backcoating layer 5. Symbols S's each indicate the formed servotrack pattern. In FIG. 3, the distance P₁ between adjacent irradiationpositions of the output laser light (L—L distance) in the images formedon the backcoating layer 5 can be expressed by using the above-describedP₀ (see FIG. 2) and the (reducing) magnification m of the condensinglens 13 (m is an integer greater than 0 and not greater than 1), beingrepresented by P₁=P₀m.

As stated above, the alignment direction of the images 25 of the outputlaser light 24 emitted from the optical fiber bundle 12 and the magnetictape 1 running direction form an angle θ. That is, line B and themagnetic tape 1 running direction A in FIG. 3 make an angle θ.Accordingly, the L—L separation with respect to the magnetic taperunning direction, i.e., the pitch Ps of the formed servo track patternsS and S is equal to P₁sin θ, which equals to P₀m sin θ. As a result, thepitch Ps of the formed servo track patterns S and S is m sin θ times thepitch P₀ of the optical fibers 11 in the optical fiber bundle 12. Inthis manner, a plurality of servo track patterns S are formedsimultaneously on the backcoating layer 5 at a pitch smaller than thepitch P₀ of the optical fibers 11 in the optical fiber bundle 12. Eachservo track pattern S is discrete and linear in the longitudinaldirection of the magnetic tape 1 as shown in FIG. 3. The shape ofadjacent servo track patterns may be the same or different. It is notalways necessary to form the servo track patterns over the whole lengthof the magnetic tape 1.

The second embodiment of the apparatus for forming servo tracks on themagnetic tape 1 is then described with reference to FIG. 4. The secondembodiment will be described only as to particulars different from theaforementioned first embodiment. The description about the firstembodiment appropriately applies to the same particulars. The members ofFIG. 4 that are the same as in FIGS. 1 through 3 are given the samesymbols.

The apparatus of this embodiment is structurally the same as that of thefirst embodiment except the servo signal writing system. FIG. 4 is aschematic plan view of the servo signal writing system according to thepresent embodiment. The condensing lens is not shown in FIG. 4. FIG. 4represents the case where the magnification of the condensing lens isset at 1.

The servo signal writing system in the apparatus of the presentembodiment has an optical fiber bundle group 16 consisting of two ormore optical fiber bundles 12 (two optical fiber bundles in the case ofFIG. 4). The optical fibers 11 in each of the optical fiber bundles 12 aand 12 b, which make up the optical fiber bundle group 16, are arrayedat a pitch P₀. The optical fiber bundles 12 a and 12 b and thecondensing lens (not shown) are disposed such that, when viewed fromabove, the alignment of real images formed of the output laser lightfrom each optical fiber bundle 12 a or 12 b through the condensing lenson the magnetic tape 1 is perpendicular to the magnetic tape 1 runningdirection A and each image is formed along the running direction A. Morespecifically, each of the optical fiber bundles 12 a and 12 b isdisposed along the magnetic tape 1 running direction A in such a mannerthat the direction of the array of the optical fibers 11 may beperpendicular to the magnetic tape 1 running direction A. The opticalfiber bundles 12 a and 12 b are superposed on each other in such amanner as to form real images at a smaller pitch than the pitch of thereal images formed by the individual optical fiber bundle. Morespecifically, the optical fiber bundles 12 a and 12 b are superposed oneach other in such a manner that the real images formed by one of theoptical fiber bundles are shifted from those formed by the other by adistance ΔP that is smaller than the pitch (=P₀ in the presentembodiment) of the real images formed by the individual optical fiberbundles (the distance ΔP equals P₀/2 in the present embodiment).

The manner of forming servo tracks by the use of the apparatus accordingto the present embodiment is explained with reference to FIG. 4. Outputlaser light emitted from the optical fiber bundle 12 a that is disposedupstream in the magnetic tape 1 running direction passes through thecondensing lens (not shown) and irradiates the backcoating layer 5 ofthe magnetic tape 1 while forming real images to form servo trackpatterns Sa, Sa . . . at a pitch of P₀. Output laser light emitted fromthe optical fiber bundle 12 b that is disposed downstream irradiates thebackcoating layer 5 of the magnetic tape 1 in the same manner whileforming real images to form servo track patterns Sb, Sb . . . at a pitchof P₀, each servo track pattern Sb being in the middle between adjacentservo track patterns Sa and Sa. Since the optical fiber bundles 12 a and12 b and the condensing lens are arranged so that the real images formedby one of the bundles and those formed by the other are shifted fromeach other by ΔP, i.e., P₀/2, the distance between every adjacent servotracks Sa and Sb also equals to ΔP, i.e., P₀/2. A plurality of servotrack patterns are thus formed simultaneously on the backcoating layer 5at a pitch smaller than the pitch P₀ of the optical fibers 11 in theoptical fiber bundle. The magnification m of the condensing lens can bemade smaller than 1 to make the servo track pitch ΔPm, which is furthersmaller than that of the above example.

An exemplary magnetic tape to which the method of the present inventionis applied and usage of servo tracks formed on that magnetic tape willbe explained briefly. The magnetic tape comprises a substrate, amagnetic or nonmagnetic intermediate layer formed on the substrate, anda magnetic layer provided on the intermediate layer as a top layer. Thesubstrate has on the other side a backcoating layer. The magnetic layerhas formed thereon a plurality of data tracks in parallel to themagnetic tape running direction. While in the above-describedembodiments the backcoating layer is used as the site capable of formingservo tracks, any other layer or the substrate may be used, or adedicated site may be provided separately.

On being irradiated with laser light, the site capable of forming servotracks undergo a physical or chemical change to form a servo trackpattern corresponding to servo signals thereby producing an opticalcontrast with the non-irradiated part. While not limiting, the means ofcausing the servo track pattern to show an optical contrast includes (1)formation of depressions having a prescribed depth on the surface of thesite, for example, the backcoating layer, 5 by irradiation with laserlight (physical change) and (2) incorporation into the site a substancecapable of color change on receipt of laser light (chemical change).

When the above-described magnetic tape is used, a head unit having apredetermined number of magnetic heads is moved across the magnetictape, switching among data tracks, to record or reproduce data on thedata track corresponding to each magnetic head, which is in accordancewith a serpentine system. Servo tracking is carried out based on theservo tracks formed on the magnetic tape so that each magnetic head maybe positioned on a right data track when a switch is made among the datatracks or during recording or reproduction. For example, the servo trackpattern is irradiated with light of prescribed wavelength, and thereflected light or transmitted light is detected to optically read theservo signals. Servo tracking is carried out based on the read servosignals in the same manner as a push-pull method, etc. that isconventionally used in the field of optical disks, etc.

Preferred conditions for forming servo tracks in the present inventionwill then be described. The running speed of the magnetic tape ispreferably as high as possible from the standpoint of productivity, but,with the ability of the running system being taken into consideration, apractically suitable speed is 1 to 5 m/sec. The output of the laserdiode is preferably 5 to 30 mW at the irradiated site for forming aservo track patterns without damaging the magnetic tape. In forming thediscrete servo track pattern S as shown in FIG. 3, the output of thelaser diode can be modified arbitrarily according to the length and theperiod of the pattern.

In order to make the track pitch smaller, it is preferred for theoptical fiber 11 to have as small a core diameter as possible becausethe core diameter is reflected on the size of the real image of theoutput laser light formed on the magnetic tape, i.e., the width of theservo track. Optical fibers whose core diameter is 3 to 9 μm that arepractically usable are preferred. In using such optical fibers, thediameter of the output laser light will be 1 to 9 μm.

The angle θ in the first embodiment is appropriately adjustableaccording to the pitch of the arrayed optical fibers 11, themagnification of the condensing lens 13, the track pitch of the servotracks to be formed, and the like.

The magnification m of the condensing lens 13 is preferably as small aspossible so as to reduce the error of the servo track pitch with respectto the angle θ. In connection to the focal depth and the aberration, itis preferably 0.3 to 0.8.

The present invention is not limited to the above-described embodiments,and various modifications can be made therein. For example, the magnetictape 1 to which the method of the present invention is applied can havea site other than the backcoating layer thereof as the site capable offorming servo tracks. In the first embodiment a plurality of opticalfiber bundles 12 may be used as regularly spaced across the magnetictape 1 as shown in FIG. 5 (in which the condensing lens is not shown).In the second embodiment, too, a plurality of the optical fiber bundlegroups 16 shown in FIG. 4 can be used as regularly spaced across themagnetic tape 1.

In the first embodiment, tilting the alignment direction of the imagesformed on the magnetic tape 1 with respect to the running direction A ofthe magnetic tape 1 can be achieved not only by tilting the opticalfiber bundle 12 itself but by tilting only the real images by means ofthe optical system, such as the condensing lens, of the servo signalwriting system.

When the optical fiber bundle group 16 shown in FIG. 4 is disposed astilted to make a prescribed angle with the magnetic tape runningdirection just like the servo signal writing system in the apparatus ofFIG. 1, it is possible to form servo track patterns on the magnetic tapeat a further reduced pitch. While in FIG. 4 the optical fibers 12 a and12 b making up the optical fiber bundle 16 are arranged close together,they may be placed apart.

Industrial Applicability

According to the present invention, a large number of servo tracks canbe formed on a magnetic tape at a small pitch simultaneously and easily.Therefore, the magnetic tape produced according to the present inventionis capable of servo control with improved accuracy, and it is possibleto increase the data track density, which will increase the recordingcapacity.

What is claimed is:
 1. A method of writing servo tracks on tape whichcomprises irradiating a first end of an optical fiber bundle comprisinga plurality of optical fibers arrayed in parallel with each other withlaser light, transmitting the laser light emitted from a second end ofthe fiber bundle as an output light source through reducing optics, andirradiating a site of the tape, said site being capable of forming servotracks, with the laser light transmitted through said reducing optics toform a plurality of servo track patterns in a running direction of thetape at a smaller pitch than the pitch of the optical fibers arrayed insaid optical fiber bundle.
 2. The method of claim 1, wherein saidoptical fiber bundle comprises the optical fibers arrayed with thecenter axes of the individual optical fibers being coplanar, andirradiation of said site with said laser light is such that thedirection in which the real images of said output light source formed onthe tape are aligned and the running direction of the tape may make anangle larger than 0° and smaller than 90°.
 3. The method of claim 1,wherein said optical fiber bundle comprises the optical fibers arrayedwith the center axes of the individual optical fibers being coplanar,two or more of said optical fiber bundles are superposed on each otherin such an arrangement that real images may be formed at a smaller pitchthan the pitch of the real images formed by the individual optical fiberbundles.
 4. The method of claim 1, wherein said reducing optics comprisea condensing lens.
 5. The method of claim 1, wherein the laser lighttransmitted through said reducing optics forms real images on the sitehaving a size equal to or smaller in size than the output light source.6. The method of claim 1, further comprising irradiating the first endof a first optical fiber in said optical fiber bundle with a first laserlight, and irradiating the first end of a second optical fiber in saidoptical fiber bundle with a second laser light.
 7. The method of claim6, further comprising controlling the first laser light with a firstcontroller and controlling the second laser light with a secondcontroller.
 8. The method of claim 1, wherein the tape is magnetic tape.9. The method of claim 1, wherein the tape runs at a prescribed speed inthe running direction as it is irradiated.
 10. An apparatus for writingservo tracks on a tape which comprises a system for running said tape, asystem for writing servo signals on said tape, and a light source systemproviding laser light incident upon said servo signal writing system,wherein: said servo signal writing system has an optical fiber bundlewhere a plurality of optical fibers are arrayed in parallel to eachother with the center axes of the individual optical fibers beingcoplanar and reducing optics which receives the laser light emitted fromthe end of said optical fiber bundle, said optical fiber bundle and saidlens being disposed such that the direction in which real images of theoutput laser light source formed through said lens are aligned and therunning direction of said magnetic tape may make an angle larger than 0°and smaller than 90°.
 11. An apparatus for writing servo tracks on atape which comprises a system for running said tape, a system forwriting servo signals on said tape, and a light source system providinglaser light incident upon said servo signal writing system, wherein:said servo signal writing system has a group of two or more opticalfiber bundles each having a plurality of optical fibers arrayed inparallel to each other with the center axes of the individual opticalfibers being coplanar, said optical fiber bundles being superposed oneach other in such a manner that real images may be formed at a smallerpitch than the pitch of real images formed by the individual opticalfiber bundles.
 12. An apparatus for writing servo tracks on a tapecomprising: a system for running said tape in a running direction; asystem for writing servo signals on said tape, the system for writingservo signals including an optical fiber bundle having a plurality ofoptical fibers arrayed in parallel with each other; and a light sourcesystem for providing laser light incident upon a first end of the fiberbundle, wherein the system for writing servo signals transmits the laserlight emitted from a second end of the fiber bundle as an output lightsource through reducing optics to form servo track patterns on the tapein the running direction at a smaller pitch than the pitch of theoptical fibers arrayed in said optical fiber bundle.
 13. The apparatusof claim 12, wherein said reducing optics comprise a condensing lens.14. The apparatus of claim 12, wherein the laser light transmittedthrough said reducing optics forms servo track patterns having a sizeequal to or smaller than the output light source.
 15. The apparatus ofclaim 12, further comprising a first laser source for irradiating thefirst end of a first optical fiber in said optical fiber bundle with afirst laser light, and a second laser source for irradiating the firstend of a second optical fiber in said optical fiber bundle with a secondlaser light.
 16. The apparatus of claim 15, further comprising at leastone controller for controlling the first laser light with a firstcontroller and controlling the second laser light with a secondcontroller.
 17. The apparatus of claim 12, wherein the tape is magnetictape.
 18. The apparatus of claim 12, wherein the optical fibers in thefiber bundle have center axes arrayed in a coplanar manner, at least twosuch optical fiber bundles are superposed on each other so that theservo tracks may be formed at a smaller pitch than the pitch of realimages formed by the individual optical fiber bundles.